Use of illicit stimulants (particularly methamphetamine) is at an alarmingly high level in certain populations of youth. Illicit stimulants are extremely habit forming and hazardous. Their use often portends an ominous future for youth who have progressed beyond gateway drugs to this hard-drug class. Yet, there is insufficient knowledge about the processes underlying the development of adolescent stimulant use. The proposed research focuses on several of the most promising processes consistently uncovered in multiple independent lines of basic research but not previously applied to adolescent stimulant use. Two sets of processes of focus are: a) spontaneous or implicit cognitive processes, which encode and activate learned associations promoting drug use;and b) protective, specific executive functions that inhibit or at least dampen the effects of such associations on behavior. These processes have been well researched in neuroscience, basic research on memory, and decision theory, and they have been increasingly applied to other drugs of abuse in a host of studies during the past several years. The present project offers a novel line of inquiry that not only studies the main effects of these processes on teenage stimulant use and use trajectories, but tests a new synergistic (interaction) model derived from recent dual-process models that receive converging support from basic research and several studies on other addictive behaviors. In addition to the advance of predictive models of drug abuse, dual-process models can help explain more specific drug patterns, for example: a) Why do some youth progress from gateway illicit drugs (e.g., marijuana) to illicit stimulants, while others from the same at-risk population appear to be protected from this progression? b) What mediates habitual levels of use and strong predictive effects of previous drug habits? c) What processes supported by extensive basic research best predict growth in stimulant use after initial trials? d) Which specific executive functions show the best protective effects on primary drugs of abuse in at-risk adolescents? To address these and other related questions, the project's major study employs a [three-wave], intensive longitudinal design using validated, primarily lab-based assessments across ages during which drug use progression to illicit stimulants is most likely in an at-risk teenage population. Despite this risk, the target population is quite amenable to mobile lab-based, computerized assessment and future intervention, as thoroughly documented in the application. The studied processes are relevant to future interventions, because they are sufficiently specific and have been delineated thoroughly in several independent lines of previous research. Thus, clear implications can emerge from the evaluation of the studied alternative models of teenage stimulant use. The integration of validated lab-based methods and processes into an "indicated" population study of youth helps the project have potentially substantial implications for innovation in theories of drug use as well as future interventions that could target the studied processes. PUBLIC HEALTH RELEVANCE: Project Narrative: Use of illegal stimulants (particularly methampehtamine) is at an alarmingly high level in certain populations of youth. This project uses theories and validated methods developed in basic research to pinpoint some of the likely causes of use of illegal stimulants and other major drugs of abuse in an at-risk youth population during ages in which onset of stimulant use is most likely. Understanding why certain youth use this drug, while others appear to be "protected" within the same at-risk population, is critical for determining how best to prevent this highly addictive and hazardous behavior.